U.S. Pat. No. 5,654,765 issued Aug. 5, 1997 to D. J. Kim and entitled "CHANNEL EQUALIZER FOR DIGITAL TELEVISION RECEIVER HAVING AN INITIAL COEFFICIENT STORAGE UNIT" is incorporated herein by reference. Kim describes a digital television (DTV) receiver capable of receiving signal transmitted via any selected one of a plurality of transmission channels, which DTV receiver includes a particular type of channel equalizer. This type of channel equalizer comprises a channel equalization filter having adaptive filtering coefficients and circuitry for calculating the adaptive filtering coefficients of the channel equalization filter by decision-feedback methods using all symbol codes. Calculating the adaptive filtering coefficients of the channel equalization filter without initial information takes a considerable amount of time. Accordingly, this type of channel equalizer further comprises a memory for storing the adaptive filtering coefficients for each transmission channel during times another channel is tuned to and during times that portions of the DTV receiver do not receive power for operating. These adaptive filtering coefficients are reapplied to the channel equalization filter when a channel is re-tuned or when power for operating is restored to all portions of the DTV receiver. This facilitates "channel surfing" by a human using a DTV receiver provided with a viewscreen.
U.S. Pat. No. 5,648,987 entitled "RAPID-UPDATE ADAPTIVE CHANNEL-EQUALIZATION FILTERING FOR DIGITAL RADIO RECEIVERS, SUCH AS HDTV RECEIVERS" and issued Jul. 15, 1998 to J. Yang, C. B. Patel, T. Liu and A. L. R. Limberg is incorporated herein by reference. Yang et alii concern themselves with digital television signals that include a training signal. Yang et alii teach that the training signal can be used to establish initial values of the adaptive filtering coefficients for the channel equalization filter, after which decision-feedback methods can be relied on. The establishment of the initial values of the adaptive filtering coefficients in reliance upon the training signal normally will bring them to desired values much faster than can be done using decision-feedback methods, and stalling of such "convergence" in false minima of the error-detection procedure is better avoided. Decision-feedback methods using all symbol codes, not just those in a training signal, are usually superior for continuing adjustment of the adaptive filtering coefficients once "convergence" has been achieved or substantially achieved. They better allow the tracking of dynamic multipath distortion.
The vestigial-sideband DTV signal that is the current standard for terrestrial DTV broadcasting is suited for use with the Yang et alii methods. This VSB DTV signal comprises data frames each composed of two fields. Each field is composed of 313 consecutive-in-time data segments. The initial data segment of each data field includes a data field synchronization code composed of a 511-sample pseudo-noise sequence (or "PN-sequence") followed by three 63-sample PN sequences. The middle 63-sample PN sequence is inverted in logic sense from one data field to the next. Portions of these initial data segments can be utilized as training signal.
While the Yang et alii methods can converge the adaptive filtering coefficients quite rapidly when multipath distortion is principally static in nature, initial convergence remains a problem when multipath distortion is dynamic. While dynamic multipath distortion usually abates after some time, tuning from one transmission channel to another will at times take longer than is desirable. Accordingly, it is attractive to store information from a time dynamic multipath distortion was not a severe problem, to be used to establish initial values of adaptive filtering coefficients when a channel is re-tuned or when power for operating is restored to all portions of the DTV receiver. Rather than storing adaptive filtering coefficients for each channel per U.S. Pat. No. 5,654,765, one may instead store the channel characterization of each channel it is first pointed out in this specification.